Pump incorporating pressure-regulated venting means

ABSTRACT

The invention provides a pump comprising at least one piston (26, 28) movable in a reciprocating manner within a chamber (12), sealing means (32a, 32b) located between the piston (26, 28) and the interior wall of the chamber (12), and venting means (36) for venting a portion of the chamber (12) bounded by the interior wall, the piston (26, 28) and the sealing means (32a, 32b), wherein the venting means (36) incorporates pressure regulating means (40) such that the pressure to which the said portion of the chamber (12) is vented can be regulated. This reduces the pressure differences across the or each sealing means and thus reduces deterioration and damage.

This application is a 371 of PCT/GB 94/02560 filed Nov. 22, 1994.

The invention relates to a pump particularly, but not exclusively, to adiaphragm pump suitable for pumping liquids.

Diaphragm pumps have been in use in industry for some years. In suchpumps, piston are caused to move in a reciprocating manner within achamber and sealing means are provided between the interior wall of thechamber and the moving piston. Sealed portions of the chamber arethereby created between the ends of the chamber and the relevant face ofthe appropriate piston. Any movement of the piston within the chambertherefore causes the pressure within that sealed portion of the chamberto change. Commonly, venting means are provided to allow the pressurewithin that portion of the chamber to return to ambient pressure atappropriate intervals during the operating cycle.

In certain instances, this venting can cause problems. For example,pumps of this type can be designed to transport liquids having internalpressures in the order of 18-28 psi created by internal carbonisation.Carbon dioxide or other gas or gas mixture supplied at a pressure of,for example, 60 psi, is introduced into the relevant portion of thechamber in order to move the appropriate piston from one operatingposition to another. When the reciprocal motion is to take place, thecarbon dioxide or other gas at 60 psi is vented to atmosphere. Thiscauses a pressure differential across the sealing means located betweenthe piston and the interior wall of the chamber. Repeated pressuredifferences of this type can cause deterioration of the sealing meanswhich must then be regularly inspected and, if necessary, replaced.

It is an object of the invention to provide a pump which does not havethe aforementioned disadvantage and which therefore has an extendedworking life and reduced maintenance costs.

The invention provides a pump as set out in claim 1 of the appendedclaims. The invention also provides a pumping system as set out in claim9 of the appended claims and a method of pumping a liquid as set out inclaim 11 of the appended claims. Preferred features of the variousaspects of the invention are set out in the subsidiary claims.

Embodiments of a pump according to the invention will now be describedwith reference to the accompanying drawings wherein:

FIG. 1 is a schematic cross-section taken through the longitudinal axisof a pump according to a first embodiment of the invention in a firstoperation position;

FIG. 2 is a schematic cross-sectional view of the pump of FIG. 1 shownin a second operating position; and

FIG. 3 is an enlarged cross sectional detail of part of a pump accordingto a second embodiment of the invention.

The pump shown in FIGS. 1 and 2 consists of a housing 10 whichincorporates an elongate chamber 12 and a transverse through chamber 14for the passage of pumped liquid. The through chamber 14 has an inlet 16and an outlet 18, between which are two parallel channels 20,22 whichcan be opened and closed by means of valves 24a,24b,24c and 24d. Thechannels 20,22 are variable in volume in their central sections by meansof the movement of pistons 26,28 which are rigidly connected byconnecting member 30. Seals 32a and 32b form liquid-tight connectionsbetween the pistons 26,28 and the interior wall of the chamber 12.

Pistons 26 and 28 are arranged so as to be reciprocatingly movablewithin the chamber 12. The movement takes place along the longitudinalaxis of chamber 12 and is controlled by means not shown in detail in theaccompanying drawings. Furthermore, gas introduction means 34 areprovided to allow the introduction of compressed gas into the chambereither to the left of piston 26 or to the right of piston 28 as desired.Venting means 36 allowing venting of these portions of the piston 12 arealso provided.

The apparatus described thus far is known. However, the venting means 36are attached to pressure regulating means in the form of a pressurevalve 40. The pressure valve 40 incorporates control means and/orsensing means designed to detect the pressure of the liquid within thechannels 20,22 or at the inlet 16 and to allow the portions of thechamber 12 to the left of piston 26 and to the right of piston 28 frombeing vented to a pressure substantially different from the pressure inthe channels 20,22. This prevents undue pressure differences occurringacross the seals 32a,32b.

The operation of the pump shown in FIGS. 1 and 2 will now be described.In the position shown in FIG. 1, piston 26,28 have just completed astroke from right to left. Valve 24a is closed and valve 24b is openhaving just allowed the liquid to be pumped to enter channel 20 from theinlet 16. Valve 24c is open and valve 24d is closed and the movement ofpiston 28 from right to left has just forced the majority of the fluidin the channel 22 through valve 24c to outlet 18. The pressure inchannels 20,22 corresponds to the internal pressure of the liquid beingpumped, e.g. 18-28 psi. The pressure in the portion of the chamber 12 tothe right of piston 28 is approximately 60 psi, this being the pressureof CO₂ or other suitable gas used to move the piston 26,28 from right toleft. The pressure in the chamber to the left of piston 26 issubstantially lower to allow the movement to have taken place.

At the completion of the stroke described above, each of the valves24a,24b,24c,24d alters its position. Valve 24a opens, valve 24b closes,valve 24c closes and valve 24d opens. Compressed CO₂ or other suitablegas at a pressure of around 60 psi is introduced into the chamber to theleft of piston 26 and a return stroke from left to right of piston 26and 28 is initiated. However, instead of the portion of the chamber 12to the right of piston 28 being vented to atmospheric pressure, thepressure regulator 40 comes into operation and allows that portion ofthe chamber to be vented only to a pressure of substantially the same asthat pressure exerted on the seal 32b by the fluid in the channel 22.This means that the pressure difference across the seal 32b isrelatively small. Damage to the seal and/or distortion of the seal 32bis thereby minimised.

When the portion of the chamber 12 to the right of piston 28 has beenvented to a suitable level, pistons 26, 28 will move from left to rightto the position shown in FIG. 2. Because of the position of the seals24a,24b, fluid previously contained in the channel 20 will be forcedthrough the outlet 18 by the movement of the piston 26. Similarly,because of the position of valves 24c,24d, fluid will be drawn intochannel 22 by the movement of the piston 28.

At the completion of this stroke, the position of each valve againreverses and compressed carbon dioxide or other suitable gas is thenintroduced into the chamber 12 to the right of the piston 28 via thecompressed gas supply means 34. The chamber 12 to the left of piston 26will be vented through the venting means 36 but, as before, the extentof the venting will be regulated by the pressure regulator 40. Again,the pressure difference across the seal 32a will be minimised.

The reduction of the pressure difference across the seals 32a,32b meansthat any damage to or distortion of the seals is kept to a minimum. Theworking life of the seals is thereby increased and maintenance costsrelating to the pump are minimised.

The pressure regulator 40 can take any suitable form. It can be arrangedto be preset in accordance with the known internal pressure of a fluidto be pumped by the pump. Alternatively, the pump can be provided withpressure sensors (not shown) inside the channels 20,22 or in thevicinity of the inlet 16 or outlet 18 to detect the internal pressure ofthe pumped fluid. In this way, the pressure to which the relevantportion of the chamber 12 is vented can be regulated in accordance withthe internal pressure of the pumped fluid.

However, FIG. 3 illustrates a regulator 50 which forms part of apreferred embodiment of a pump according to the invention. The regulator50 would replace the regulator 40 shown in FIGS. 1 and 2 and can be usedin conjunction with a pump having all of the remaining features of thepump shown in FIGS. 1 and 2. The regulator 50 comprises an upper portion52 which can be arranged to be connected to the inlet 16 of the pump. Ifdesired, the upper portion 52 can be formed integrally with the inlet 16or can be connected thereto by suitable connecting means (not shown).The upper portion 52 includes a fluid inlet 54 which is intended to beconnected to a supply or reservoir of fluid to be pumped by the pump.The regulator 50 also comprises a lower portion 56 which includes anexhaust gas inlet 58 and an exhaust gas outlet 60.

Between the upper and lower portions 52,56 is located a movable shut-offvalve 62 comprising a central pin 64 and a flexible diaphragm 66. Thediaphragm 66 is fixedly connected to the wall of the regulator 50 and tothe central pin 64. The central pin 64 extends downwardly from thediaphragm 66 towards the exhaust gas outlet 60 and, in the positionshown in FIG. 3, the end of the central pin 64 rests in the entrance tothe exhaust gas outlet 60. An O-ring seal 68 is provided between thecentral pin 64 and the entrance to the exhaust gas outlet 60 such that,when the end of the pin 64 rests in the outlet 60, a gastight seal isproduced. However, when an upward force is exerted on the shut-off valve62, the valve 62 can move upwardly so that the central pin 64 moves outof engagement with the entrance to the exhaust gas outlet 60 and thusthe gastight seal provided by the O-ring seal 68 is broken. Any upwardmovement of the shut-off valve 62 is limited by the diaphragm 66.

The operation of the regulator 50 is as follows. Fluid to be pumped bythe pump is introduced to the inlet 16 via the upper portion 52.Specifically, the supply or reservoir of fluid to be pumped is connectedto the fluid inlet 54. The fluid then fills the upper portion 52 of theregulator 50 above the shut-off valve 62. The internal pressure of thefluid to be pumped is therefore exerted on all of the internal surfacesof the upper portion 52, including the upper surface of the diaphragm 66and the central pin 64. The venting means 36 (see FIGS. 1 and 2) areconnected directly to the exhaust gas inlet 58 by means of a pipe 70.Gas which is vented or exhausted from the portion of the chamber 12either to the left of piston 26 or to the right of piston 28 is thuspassed directly to the lower portion 56 of the regulator 50. Thepressure of the vented gas is therefore exerted on all of the internalsurfaces of the lower portion 56, including the lower surface of thediaphragm 66 and the central pin 64.

When the pressure of the vented gas in the lower portion 56 exceeds theinternal pressure of the fluid to be pumped, the shut-off valve 62 israised thus opening the entrance to the exhaust gas outlet 60. Theexhaust or vented gas thus has a free passage out of the regulator 50via the outlet 60. If, however, the pressure of the exhaust gas dropsbelow the internal pressure of the fluid to be pumped, the shut-offvalve 62 will drop to the position shown in FIG. 3, ie. with the lowerend of the central pin 64 in engagement with the entrance to the exhaustgas outlet 60. The outlet 60 is thereby sealed thus preventing anyfurther escape of vented gas. Only when the pressure of the exhaust gasagain exceeds the internal pressure of the fluid to be pumped will theoutlet 60 be re-opened to allow the exhaust gas to escape. The exhaustgas is thereby maintained substantially at the internal pressure of thefluid to be pumped.

It will be appreciated that, if desired, biasing means can beincorporated into the regulator 50 so as to bias the shut-off valve 62in one direction or another. The effect of this would be to maintain thepressure of the exhaust gas a little above or below the internalpressure of the fluid to be pumped depending upon whether the biasingwere downward or upward.

It is envisaged that a pump of the type indicated above can be includedin a pumping system suitable for use in any situation such as, e.g. abrewery or public house or any other industrial situation. When thesystem is intended for use in pumping beverages, the pump will bedesigned to handle liquids having internal pressures of between 7 and 30psi although liquids having higher internal pressures can preferably behandled. The pumping system will incorporate known means for connectingthe inlet 16 of the pump to a reservoir of a liquid, e.g. beer or otherbeverage, and the outlet 18 of the pump will be connected to aconventional dispenser. It is envisaged that a pumping system of thistype could incorporate a plurality of pumps as described above and thesepumps could be connected to individual dispensers if desired. If aplurality of pumps is provided, they could be supplied by a singlereservoir or from separate reservoirs of liquid.

It will be appreciated that the invention is not limited to theembodiments described above but encompasses any and all variations whichwill be apparent to a reader skilled in the art.

I claim:
 1. A pump comprising:a chamber having an inlet and an outlet,the inlet and the outlet being opened and closed by valve means for thepassage of a pumped fluid; at least one piston movable in areciprocating manner within said chamber; sealing means located betweenthe piston and the interior wall of the chamber; introduction means forintroducing a working fluid into a portion of the chamber bounded by theinterior wall of the chamber, the piston and the sealing means; andventing means for venting the portion of the chamber so that alternateintroduction of the working fluid into, and venting of the working fluidfrom, the portion of the chamber causes the piston to move in areciprocating manner to transport the pumped fluid through the chamberfrom the inlet to the outlet, wherein the venting means incorporatespressure regulating means to regulate, in dependence upon the pressureof the pumped fluid, the pressure to which the said portion of thechamber is vented such that, in use, the pressure of the working fluidin the said portion of the chamber is prevented from falling, duringventing, below the pressure of the pumped fluid in the chamber.
 2. Apump as claimed in claim 1, wherein the pressure regulating meanscomprise sensors for sensing the pressure of the fluid being pumped bythe pump and means for controlling the regulated pressure in accordancewith the pressure sensed by the sensors.
 3. A pump as claimed in claim1, wherein the regulating means comprise a movable shut-off valveresponsive in use to the difference between the pressure within the saidportion of the chamber and the pressure of the pumped fluid in thechamber.
 4. A pump as claimed in claim 3, wherein the movable shut-offvalve is movable between an open position allowing venting of the saidportion of the chamber and a closed position preventing venting of thesaid portion of the chamber, the valve being moved from the openposition to the closed position when, in use, the pressure in the saidportion of the chamber drops below the pressure of the pumped fluid inthe chamber.
 5. A pump as claimed in claim 4, wherein the movableshut-off valve comprises a diaphragm exposed, in use, on one side to thefluid being pumped by the pump and on the other side to the ventedcontents of the said portion of the chamber.
 6. A pump as claimed inclaim 1, wherein two pistons are located in the chamber.
 7. A pump asclaimed in claim 1, wherein the sealing means comprise at least onerolling diaphragm seal.
 8. A pumping system for pumping a fluid from atleast one reservoir to at least one dispensing point, said systemcomprising at least one pump and attachment means for connecting said atleast one pump to said at least one reservoir, said at least one pumpcomprising:a chamber having an inlet and an outlet, the inlet and outletbeing opened and closed by valve means for the passage of the pumpedfluid; at least one piston movable in a reciprocating manner within saidchamber; sealing means located between the piston and the interior wallof the chamber; introduction means for introducing a working fluid intoa portion of the chamber bounded by the interior wall of the chamber,the piston and the sealing means; and venting means for venting theportion of the chamber so that alternate introduction of the workingfluid into, and venting of the working fluid from, the portion of thechamber causes the piston to move in a reciprocating manner to transportthe pumped fluid through the chamber from the inlet to the outlet,wherein the venting means incorporates pressure regulating means toregulate, in dependence upon the pressure of the pumped fluid, thepressure to which the said portion of the chamber is vented such that,in use, the pressure of the working fluid in the said portion of thechamber is prevented from falling, during venting, below the pressure ofthe pumped fluid in the chamber.
 9. A pumping system as claimed in claim8, wherein a plurality of dispensing points are provided and a separatepump is associated with each dispensing point.
 10. A method of pumping afluid using a pump, the pump comprising:a chamber having an inlet and anoutlet, the inlet and outlet being opened and closed by valve means forthe passage of the pumped fluid; at least one piston movable in areciprocating manner within said chamber; sealing means located betweenthe piston and the interior wall of the chamber; introduction means forintroducing a working fluid into a portion of the chamber bounded by theinterior wall of the chamber, the piston and the sealing means; andventing means for venting the portion of the chamber so that alternateintroduction of the working fluid into, and venting of the working fluidfrom, the portion of the chamber causes the piston to move in areciprocating manner to transport the pumped fluid through the chamberfrom the inlet to the outlet, wherein the venting means incorporatespressure regulating means to regulate, in dependence upon the pressureof the pumped fluid, the pressure to which the said portion of thechamber is vented such that, in use, the pressure of the working fluidin the said portion of the chamber is prevented from falling, duringventing, below the pressure of the pumped fluid in the chamber, themethod comprising the steps of causing said at least one piston to movewithin the chamber, and venting said portion of the chamber, wherein theventing is regulated, in dependence upon the pressure of the pumpedfluid, so as to maintain the pressure in the said portion of the chambersubstantially at the pressure acting on the sealing means on the sidethereof remote from the said portion of the chamber.
 11. A method asclaimed in claim 10, wherein carbon dioxide gas is used to causereciprocating movement of said piston within said portion of thechamber.